William Ellery Channing (1780 – 1842) was the foremost Unitarian preacher in the United States in the early nineteenth century and along with Andrews Norton, (1786-1853), one of Unitarianism's leading theologians. He was known for his articulate and impassioned sermons and public speeches, and as a prominent thinker in the liberal theology of the day.

Channing's religion and thought were among the chief influences on the New England Transcendentalists, though he never countenanced their views, which he saw as extreme. The beliefs he espoused, especially within his "Baltimore Sermon" of May 5, 1819, at the ordination of a future famous theologian and educator in his own right, Jared Sparks, (1789-1866), as the first minister (1819-1823) of the newly organized (1817) "First Independent Church of Baltimore" (later the "First Unitarian Church of Baltimore (Unitarian and Universalist)").

Here he espoused his principles and tenets of the developing philosophy and theology of "Unitarianism" resulted in the organization later in 1825 of the first Unitarian denomination in America (American Unitarian Association) and the later developments and mergers between Unitarians and Universalists resulting finally in the Unitarian Universalist Association of America in 1961.

In later years Channing addressed the topic of slavery, although he was never an ardent abolitionist. Channing wrote a book in 1835, entitled, "SLAVERY" James Munroe and Company, publisher. Channing, however, has been described as a "romantic racist" in "Black Abolitionism: A Quest for Human Dignity" by Beverly Eileen Mitchell (133–38). He held a common American belief about the inferiority of African people and slaves and held a belief that once freed, Africans would need overseers. The overseers (largely former slave masters) were necessary because the slaves would lapse into laziness. Furthermore, he did not join the abolitionist movement because he did not agree with their way of conducting themselves, and he felt that voluntary associations limited a person's autonomy. Therefore, he often chose to remain separate from organizations and reform movements. This middle position characterized his attitude about most questions, although his eloquence and strong influence on the religious world incurred the enmity of many extremists. Channing had an enormous influence over the religious (and social) life of New England, and America, in the nineteenth century.